It's always a big mystery how much money the children of billionaires have at their disposal—or will have some day. The existence and size of trusts is nearly impossible to determine, and even heirs may not know what is in their parents' wills. Wealthy families rarely talk publicly about the intergenerational transfer of wealth.

Also, wealthy parents have wildly varying approaches to handing down their fortunes. Some give generously and early to their children; others barely give anything at all, even after they die.

Thus, as George Soros moves further into his 80s with a fortune of over $20 billion, it's anyone's guess what kind of money his five children will ultimately inherit. Likewise, it's hard to say how much money they already have.

But there are a few hints about the wealth of Soros's five children. Alexander Soros has given away over $500,000 for electoral and philanthropic causes in the past few years. Jonathan Soros has also given heavily in both spheres.

But of all Soros's children, Andrea Soros Colombel is the most far along in her philanthropic career. In 1993, after a period of travel in China and working as an English teacher on the Tibetan Plateau, Andrea started the Trace Foundation, which for nearly twenty years "has supported the continuity and development of Tibetan culture, language and places, while improving lives and strengthening communities on the Tibetan Plateau," according to its website.

The Trace Foundation had just over $20 million in assets in 2011—most of which seems to have been donated by Andrea Soros Colombel herself, according to tax records. Meanwhile, Andrea and her husband Eric Colombel have enough money sitting around that they could make a $1 million gift to the ACLU in 2010. Oh, and in 2012, her townhouse in Greenwich Village went on the market for $29.5 million. She owns other real estate in the Village, too.

This is one rich woman. And she is likely to become much, much richer some day. Eric Colombel also comes from some money, although less is known about him.

But back to Tibet. Andrea Soros's giving in this area appears to be a textbook example of smart philanthropy. She chose a relatively narrow focus (and one that wasn't especially trendy at the time) and has stuck with it for nearly two decades. Moreover, the Trace Foundation has pulled nearly every lever it can to help Tibetans and preserve their culture. During its first decade, the foundation made grants to international and local NGOs working with Tibetans. But starting in 2004, it has implemented its own projects—which Soros Colombel says ensures greater accountability.

The foundation's work is multi-dimensional and has included hands-on community development, scholarships for Tibetan students, and an array of efforts to aimed at documenting and bolstering Tibetan culture. That last point, about culture, is notable in an era where global development philanthropy tends to be dominated by bean counters. As Soros Colombel explains:

Development is, fundamentally, about improving quality of life. While it is critical to focus on the more tangible aspects of what this means -- access to education, clean water, economic opportunity, and so forth -- the human experience goes beyond these tangibles. Connection to culture is an integral part of well-being, especially when cultural history and community ties run as deep as they do in Tibetan regions of the world. For this reason, the Foundation’s projects focus on the nexus of culture and development and look for ways to reinforce both; we believe that culture and development must advance hand in hand.

Early this month, the foundation teamed up with the Heller School at Brandeis to create a new scholarship for a Tibetan inside Tibet working on women’s leadership for development on the Tibetan Plateau.

There's also another foundation in the mix: the Tsadra Foundation, which Soros and Colombel created together in 2000, after Colombel came into his inheritance. (It's now mainly funded by the Trace Foundation.) Tsadra awards scholarships for "both advanced Buddhist studies and advanced contemplative training." It also has a small research staff based in Boulder, Colorado, and headed by Marcus Perman, who's an expert in Tibetan Buddhism. Elizabeth Callahan, Tsadra's director of studies, has been studying Buddhism for 35 years and is a leading translator of Buddhist texts.

These folks are heavyweights in this world, and Tsadra makes clear they only fund people with "many years of contemplative and scholarly experience in Tibetan Buddhism." Don't knock on this door unless you're well along in, um, your journey. Also keep in mind that Tsadra's funds are limited, and most of the scholarships they give out are under $10,000.

Tsadra's biggest grants have gone for translation, and it has funded a "new series of digital books and apps featuring the most important texts for the study and practice of Tibetan Buddhism." Yup, Tsadra are the folks bringing Buddhist classics to your iPad. They've published 418 Tibetan books, and dozens of western ones, too.

Tsadra is focused on advancing Buddhism in the West, so it's not working on the ground on Tibet. Through its translation and publishing work, though, it's made an important contribution to the preservation of Tibetan and Buddhist culture. Again, this strikes me as smart philanthropy, especially for a funder who wants to make a difference but doesn't have limitless cash: Pick a very specific but overlooked niche, and then drill away for years.

Just so you know, Andrea Soros Colombel is not "all Tibet, all the time." She's built on her experience working in Tibetan areas to contribute to other philanthropic efforts in the developing world. She was a founding partner of the Acumen Fund, and remains a deeply involved board member. Acumen is a nonprofit venture fund that backs entrepreneurial projects that promote development. Over its first decade, it directed investments of $73 million into 65 ventures designed to serve the poor. The Acumen Fund sees itself as "reinventing philanthropy" through its venture approach.

Andrea Soros Colombel is still in her forties and has yet to access the bulk of the inheritance that is likely to come her way. Judging by her track record so far, she is likely to do some pretty big things in the future if and when she gets her hands on big money.